Dr. Kenjiro Shimano
How to contrast the greenhouse effect
"come combattere l'effetto serra"
Ladies and gentlemen, thank you for coming tonight.
I am going to talk about one of the most important and serious
environmental problems.
It is very significant that such a lot of people pay attention
to the global environment.
Since the mid 1980's possibility of global warming has been
pointed out.
Today most of people share consensus that the negligible
temperature rise will occur if we, human beings, continue to emit
greenhouse gases.
At first I explain what the greenhouse effect is.
In this figure, the energy budget of the earth is schematically
explained.
The sunshine consists of rays of various wavelength;
from ultraviolet to infrared. These rays convey energy from the
sun to the earth. In turn the earth radiates infrared rays outward.
Roughly speaking these incoming and outgoing energy fluxes keep
the balance and the average surface temperature of the earth is
always kept around 15 degrees centigrade.
On the other hand, there is absorption of energy by the atmosphere.
For example, water vapor (H2O gas), carbon dioxide (CO2) and methane
(CH4) absorb part of the infrared radiation from the earth.
The energy absorbed by these gases stays within the atmosphere and
heats the air and the ground. It is called "greenhouse effect".
This estimation shows how strong the effect is; without these gases
the average surface temperature would be about -23 degrees
centigrade and the whole world would be like the arctic region.
Now imagine. If the concentration of greenhouse gases increases,
what will happen?
Much more energy will be absorbed in the atmosphere and it will
result in rise of the earth temperature. It is a mechanism of
global warming.
Here we focus on carbon dioxide (CO2) because its contribution to
global warming is bigger than other greenhouse gases.
Without doubt huge amount of CO2 has been emitted by human
activities since the industrial revolution.
It is attributed to use of fossil fuel such as petroleum and coal.
Before the industrial revolution CO2 concentration in the
atmosphere was about 280ppm but it has already reached 360ppm.
CO2 in the atmosphere has been obviously increasing.
We are afraid of temperature rise caused by CO2.
A lot of researchers have reported that also the earth temperature
was rising.
There is the oscillatory property of the temperature change.
However, the average has the tendency of increasing.
The average temperature rise after 1860s is said to be in the range
between 0.3 and 0.6 degrees centigrade.
CO2 emission due to human activities is increasing.
The rate of global warming should be accelerated.
We will see enormous damages unless we take some measures
to cope with it.
As long as I know, two kinds of scientific efforts have been made
with regard to global warming. One is prediction and the other is
prevention or slowdown of warming.
In the predictive research, various quantities in the future are
evaluated such as CO2 concentration, temperature, height of sea level
rise and so on.
It is a kind of computer simulation.
Exact prediction of such quantities is very difficult because
there are a lot of unknown physical processes.
For example, essential part of CO2 behaviour still remains unknown.
Gas exchange between the ocean and the air holds a large part in
the CO2 budget, however its phenomenon is not fully clarified.
Its evaluation is made through a model derived from limited
observations and researchers' physical intuition.
Every simulation result reported so far includes uncertainty.
different results have been reported by different researchers
for the same problem.
Look at these predictions of the temperature and the sea level rise.
Without doubt they include uncertainty, but they are approved by many
researchers as they seem more accurate than other results.
In other words, they are most reliable evaluations at present.
If we don't take any measures against global warming, the temperature
and the sea level rise will reach 2 degrees centigrade and 48cm
respectively in the year 2100.
You may think these values are small, but they are large enough to
change the climate of our planet, and large enough to change the
society and our way of life.
Of course most of us will have passed away 100 years later,
but we are definitely responsible for the future of our children
and grandchildren, aren't we?
Now let's consider damages brought about by global warming.
There are many expected influences and damages.
At first, climate change is expected. Climate change itself is not
a big threat.
You can cope with it only by taking off your jacket.
However it is accompanied with disastrous influences.
One example is spread of tropical diseases such as malaria.
The region of the tropical climate will be enlarged by the
temperature rise.
Some researchers have reported that about 70 million people in
the world would be newly infected with malaria by global warming.
Here is a prediction about potential danger of malaria infection.
There is no danger of malaria infection in Europe today.
But, if CO2 concentration is doubled, you must face the danger of
malaria even here in Italy.
Other influences are listed here, possibility of stronger cyclone
and typhoon, change of ocean currents and tides, damage on fishing
industry, flora change, ecosystem change, agricultural damage and
food shortage crisis as a consequence.
As for food shortage, Japanese people had a bad experience 6 years
ago when there was 30 % decrease of rice production.
The whole nation of Japan was in a panic.
We are afraid of the same situation in the future.
I think you have concern about wheat.
Unfortunately wheat doesn't have strong tolerance to fever.
In India and Bangladesh, more than 50% decrease of wheat production
in 2100 is expected.
I cannot predict how large the influence will be here in Italy,
but more or less you will not be free of it.
I hope your grandchildren will be able to eat delicious pasta
everyday as you do today.
The second problem is sea level rise that will be caused by
melting of icesheets, mountain ice caps and glaciers.
Thermal expansion of the ocean water is said to be another reason.
You can see that the sea level has been rising since the last century.
Global sea level rise over last 100 years is estimated at the range
between 10 and 20cm.
Influences of sea level rise are obvious; loss of coastal lands,
disappearance of agricultural, commercial, industrial and residential
areas, loss of industrial properties and loss of cultural heritages.
Damages by the sea level rise will be very serious.
In this figure, submerged areas in Bangladesh is shown as dark blue
for the case of sea level rise by 1 meter.
n India estimated economical damages amount to 71 billion US dollars
in total (about 130 trillion lire) including the cost of land loss,
displacement of population and households, damage to road networks
and so on.
n Italy, everybody is concerned over submergence of Venice.
It will be a great damage on tourism of this country.
No one knows where to go for a honeymoon.
You understand how serious the problem is.
e must take measures to avoid the worst scenario.
Now let's turn to how to prevent or slowdown global warming.
The only way is to reduce the total amount of CO2 emission.
O2 emission due to human activities is about 10 billion tons a year.
Advanced nations have decided to achieve 5% reduction by the year 2010.
But this level of reduction is not sufficient enough.
Further reduction is said to be necessary.
There are a lot of measures and proposals to reduce CO2 emission
such as use of bio-mass fuel, use of wind power and use of bicycles
instead of motorcars.
I think you are familiar with some of such ideas, so I don't explain
them here but I would like to present the concept of "efficiency".
Do you know how long your car runs by burning 1 liter of fuel?
My car runs 11 or 12km by 1 liter of gasoline, so I should burn about
2 liters when I drive to Sansepolcro from Citta di Castello.
However, if I had a perfect engine, I could drive just to Ravenna
with 2 liters of gasoline.
I can get 8600 kilo-calories of energy or heat from 1 liter of
gasoline, but only 20% is utilized for driving my car.
The other 80% is wasted.
This value, 20%, is efficiency of my engine.
I don't mean my car is a jalopy at especially low efficiency.
Efficiency of your cars is at the comparable level.
The point is that technology of today cannot extract the full
potential of fossil fuel.
According to thermodynamics it is theoretically impossible to
develop a perfect engine, but we can develop engines of higher
efficiency than 20%.
Imagine an engine of 40% efficiency, twice as high as my car.
You will be able to get to Sansepolcro with only 1 liter of
gasoline and, of course, CO2 emission will be reduced to the half.
If all the power systems in the world are replaced by those of
twice as high efficiency, CO2 emission will be reduced to the half
and the global warming and climate change problem will be resolved.
Now I am going to present examples of high efficiency power systems.
Low CO2 emission cars have been already developed and available.
This car has two power sources, a gasoline engine and an electric motor.
Efficiency of the gasoline engine changes according to rotating speed
and power output.
When you drive on a highway (autostrada), your engine is running near
the highest efficiency point.
To the contrary, when you drive through a traffic jam in a big city,
your engine is forced to run at a low efficiency.
However, in this new car, the engine is always running near the highest
efficiency point.
The car is driven by the electric motor when you go slowly.
The engine does not drive wheels but generates electricity for the motor.
Rotational speed of the engine is independent of the vehicle speed
because there is no direct connection between the engine and wheels.
You can drive this car to Sansepolcro with only 1 liter of gasoline.
Higher efficiency is required not only for motorcars but also for
other machines such as gas turbines used in power plants and jet planes.
Efficiency of gas turbines is approximately 40%.
Engineers like me and my students make this kind of efforts to
develop turbo machines of high efficiency.
Another proposal to save fossil fuel is the co-generation system.
In electricity generators used in power plants, heat is always
generated.
The efficiency of power plants is about 40% because the generated heat
is thrown away.
But in the co-generation system the heat is used for other purposes
such as hot water supply and space heating with warm air.
Of course its efficiency is very high; the average is 80% and
the highest exceeds 90%.
Usually power plants are located far from cities and
residential areas.
But for efficient use of the heat, co-generation plants should
be settled in commercial, residential and industrial areas.
In the future each house will be equipped with its own
co-generation system.
Tonight I presented some examples of technical challenges
for resolution.
These new engines and systems are still expensive today and
all the people or all the companies cannot afford them.
But I believe that cost reduction will be achieved in the near future.
We don't have to be pessimistic about global warming because
technical solutions will be offered soon.
It is very important for us to be careful of energy efficiency.
Please always consider if efficiency of your machine is high or
low and select a system of high efficiency.
I believe gathering of such efforts will save the earth.
The future of the planet depends on each of us.
To conclude the talk I present something encouraging.
There is a project of CO2 disposal into the deep ocean.
If CO2 is put into the sea at the depth of 2000m, CO2 will stay
in the sea for several hundred years.
In the project, huge amount of CO2 from power plants will be
gathered and disposed into the sea.
The project is technically realizable now but it has not done
yet because influences on the ecosystem in the sea are still unknown.
The environmental assessment of CO2 disposal is one of my
research subjects.
Now let me say again "the future of the earth depends on each of us".
My students and I do our research, and you, please pay attention
to energy and its efficiency.
Thank you for attention.
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